An apparatus which corrects tone pitches of a given tone waveform is known in the art such as a pitch corrector or a pitch changer which corrects the tone pitches of a given tone waveform to arbitrarily designated note pitches (i.e. tone frequencies) in a musical scale. See, for example, unexamined Japanese patent publication No. H1O-78791 (now issued U.S. Pat. No. 3,379,348). Such an apparatus is used mainly for correcting unstable or incorrect musical instrument tones or singer's voices fluctuating or deviating in tone pitch to produce a refined musical performance. For example, the apparatus may be used to adjust the singer's vocal tone pitches to the correct pitches of the accompaniment at a karaoke place. Or alternatively, the apparatus may be used to emphasize the characteristic features of the performed tones or voices by intentionally fluctuating or deviating the pitches in order to highlight the performers performance. A pitch corrector is capable of processing musical tone wave signals in real time. Some devices are provided in the form of a function expanding plug-in software for an automatic music performing apparatus. For example, a pitch corrector may be useful in the case of recording vocal tones (i.e. human voices of a singer) accompanied by an automatic musical performance so that the pitches of the vocal tones should be corrected to the predetermined melody note pitches (or to the accurate note pitches in the predetermined musical scale) to realize voices singing in accurate note pitches to match the accompaniment.
Such an apparatus or software product like a pitch corrector or pitch changer for correcting the pitches of the given tone waveform should have a function of detecting the note pitches of the given or inputted tone waveform. A typical pitch detecting procedure is to form an envelop waveform from the given tone waveform data, to detect the zero crossing points (the points where the wave shape crosses the zero level from a positive area to a negative area or from a negative area to a positive area) of the envelope waveform, and then to recognize the period (time span) between each adjacent zero cross points to determine the period of the given tone waveform.
A conventionally known pitch correcting apparatus or software product, however, did not include a device for visually recognizing how each tone pitch was corrected, and so forth. Further, a conventional apparatus which forms an envelope waveform of the input tone waveform and merely measures periods (time span) between respective zero cross points would inevitably involve errors due to noise vibrations or higher harmonics vibrations contained in the input tone waveform in the vicinity of the zero level.